I was wondering about how a taught wire might be used for measurements and very much like the arrangement John describes. I have a box full of Arduinos waiting for something to do.
Joe, One idea to throw into the melting pot... If two wires are stretched one above the other, separated by a distance slightly less than the diameter of the laser beam (wrapped around two suitably chosen drill shanks for example), can your sensor be used to accurately show the relative illumination of the two wires as the beam moves horizontally along them? Quite small variations of height might show up as significant variations of illumination brightness or width on the wires.

Kit